UV radiation curable transparent conductive compositions are applied to a substrate through spraying, screen printing, dipping or brushing, thus forming a transparent conducting film or coating. Transparent conductive coatings transmit visible light while possessing electrical conductivity. Accordingly such coatings find application in automobiles, airplanes, etc. as electrodes for liquid crystal devices, exothermic resistors, and photosemiconductors.
UV curable conductive films offer advantages over typical heat curable films typically produced by chemical vapor deposition, sputtering, and sol-gelling. Heat curable compositions used for example in the sol-gel process require the use of organic solvents that contain a significant amount of volatile organic compounds (VOCs). These VOCs escape into the atmosphere while the heat curable composition dries. Such solvent based systems are undesirable because of the hazards and expenses associated with VOCs. The hazards include water and air pollution and the expenses include the cost of complying with strict government regulation on solvent emission levels. In contrast, UV curable compositions contain reactive monomers instead of solvents; thus eliminating the detrimental effects of the VOCs.
The use of heat curable compositions not only raises environmental concerns but other disadvantages exist with their use as well. Heat curable compositions suffer from slow cure times which lead to decreased productivity. These compositions require high energy for curing due to energy loss as well as the energy required to heat the substrate. Additionally, many heat curable compositions yield poor film properties that result in decreased value of the end product.
Although UV curable compositions exhibit superior properties and performance over their heat curable counterparts, UV curable compositions themselves suffer from certain disadvantages. Generally, UV compositions have high molecular weights and a substantial degree of cross linkage due to the highly reactive nature of the composition. As a result, many of these compositions suffer from low durability and resin shrinkage. With the use of many such compositions, an inordinately high amount of UV light is required to cure. With some compositions, suspended solids fall out of solution after a period of one to two days. This dispersion adversely affects the gloss and clarity of the finished product.
Accordingly, there exists a need to provide environmentally safe UV curable transparent conductive compositions which exhibit improved appearance and workability. Additionally, there is a need to provide a method of applying an improved composition which furthers the goal of improved performance.